1. Field of the Invention
The present invention relates to a semiconductor light-emitting element comprising a light-transmitting metal electrode provided with fine openings, and also relates to a process for production thereof.
2. Background Art
A metal electrode is generally employed as an electrode provided on a semiconductor layer in a semiconductor light-emitting element. If produced from metals by the alloying process, the electrode is brought into such good ohmic contact with the semiconductor layer that a great deal of electric current can be injected into an active layer. Further, because of low contact resistance, the resultant device can work stably.
However, in the case where a metal electrode is adopted, a light-emitting area is small because the electric current flows only just under the electrode or near there. Further, it is also a problem that light emitted from the active layer is shaded by the opaque metal electrode. As a result, the light-extraction efficiency of the semiconductor light-emitting element is too lowered to give off a sufficient amount of emission. In order to solve the problem, there are proposed methods for enlarging the light-emitting area by incorporating fine wires into a pad-electrode and for expanding the electric current distribution by forming a current-spreading layer between the electrode and the semiconductor layer. However, they are yet to succeed in obtaining sufficient intensity of emission given off from the whole surface.
Recently, it has been studied to adopt an electrode structure in which a layer of transparent conductive oxide such as ITO and ZnO is formed on the light-extraction side-whole surface of the semiconductor layer and a metal pad-electrode is further formed thereon. In this method, it is possible to inject the electric current evenly and to extract out the light from the whole surface (see, JP-A 2005-209734 (KOKAI), for example).
However, in the electrode comprising the transparent conductive oxide, the semiconductor layer is in such poor ohmic contact with the electrode layer that the contact resistance is higher than that of the metal electrode (see, T. Margalith et. al., Appl. Phys. Lett. 74, 3930 (1999), for example). Further, it is also a problem that the transparent conductive oxide layer shows poorly adhesion to the metal electrode.